Human hearing is generally considered to be in the range of 20 Hz to 20 kHz, with greatest sensitivity to sounds including speech in the range of 1 kHz to 4 kHz. Most people naturally learn at a young age to differentiate and distinguish between different sounds, particularly sounds used frequently in the particular language commonly spoken around that young person. As people age, often their hearing slowly deteriorates, often with high frequency hearing or hearing of particular sounds decreasing more significantly than low frequency or other particular sounds. Hearing aids, personal sound amplifier products (“PSAPs”) and similar hearing assist devices are used by many people to increase/adjust the amplitudes (and perhaps frequency) of certain tones and sounds so they will be better heard in accordance with their hearing loss profile. Cochlear implants, which output an electrical pulse signal directly to the cochlea rather than a sound wave signal sensed by the eardrum, are another type of hearing assist device which may involve customizing the signal for an individual's hearing loss or signal recognition profile.
For many years, the consensus approach used by hearing aid manufacturers and audiologists has been to focus on seeking perfect sound-quality that adjusts the gain and output to the individual hearing loss of their patients. Audiologists commonly perform a “fitting” procedure for hearing assist devices, and patients usually visit a hearing aid shop/audiologist to get the initial examination and fitting. The hearing aid shop/audiologist takes individual measurements of their patients, often measuring the hearing loss profile of the person being fitted, and taking additional measurements like pure tone audiometry, uncomfortable loudness of puretones, and speech audiometry. Using proprietary or standard algorithms, the audiologist then attempts to adjust the hearing aid profile of various parameters in the hearing assist device, usually within a digital signal processor (“DSP”) amplifier of the hearing assist device. For instance, primary parameters which are adjusted in fitting a particular DSP amplifier (an OVERTUS amplifier marketed by IntriCon Corporation of Arden Hills, Minn.) include overall pre-amplifier gain, compression ratios, thresholds and output compression limiter (MPO) settings for each of eight channels, time constants, noise reduction, matrix gain, equalization filter band gain settings for each of twelve different frequency bands, and adaptive feedback canceller on/off. The typical fitting process usually involves identifying the softest sound which can be heard by the patient at a number of different frequencies, optionally together with the loudest sound which can be comfortably heard by the patient at each of those frequencies.
With all of these various parameter settings which can be adjusted by the audiologist during fitting, there are millions of different audio signal transfer functions which can be achieved with any particular DSP-based hearing aid. If the hearing impaired person has no measurable hearing in some frequencies, the audiologist commonly minimizes or eliminates those frequencies in the output so as to provide the greatest signal to noise ratio (i.e., to provide the most information) in the frequencies that the hearing impaired person has measurable hearing. That is, the consensus approach is to eliminate sounds output in so called “dead regions”, and thereby eliminate background noise that could detract from intelligibility. In addition, hearing aid manufacturers and/or audiologists use several features (like automatic reduction of low frequency gain, etc.) to keep the acceptance level of users high. While audiologists can be provided guidelines and default settings that make fitting easier, audiologist fitting of the hearing aid and selecting each of these different parameter values tends to be more of an art than a science.
More recently, hearing aid manufacturers have added the capability of hearing aids to use wireless accessories such as external microphones and connections to smartphones to increase the usability of their hearing aids in different listening situations. These new capabilities still retain the focus on providing an objective “best” quality sound and signal to noise ratio, assuming that the entire hard-of-hearing problem is in the degradation of the ear to convert sound into a single “best” signal fed to the user's brain.
Even with the plethora of advances in modern hearing assist devices, many users find even high quality hearing aids to be unacceptable in improving their hearing sufficiently back to their memory of better hearing and understandability of speech and other sounds in differing listening environments. Many users are unsatisfied with the performance of their hearing assist devices, either as not optimally fitted, or as the hearing assist device is used in different environments with sound profiles and voices which differ from those used by the audiologist during fitting, or as the device gets dirty or device performance otherwise degrades during use. Particularly for users having a hearing loss in the range of 30-50 decibels in the critical speech containing frequencies, current fitting methods, even with a high quality hearing aid and professional assistance, do not allow the user to sufficiently understand speech, particularly in a noisy environment, to the same degree they could at a younger age. Better fitting methods are needed.